Hello,
Use this code to enable Quotes in your org. I was write this code for enable Quotes in my developer org:-
 

public class EnableQuotes {  

    public void fetch()
    {
        HttpRequest request = new HttpRequest();
        request = new HttpRequest();
        request.setEndpoint('https://ap2.salesforce.com/services/Soap/m/31.0');
        request.setMethod('POST');  
        request.setHeader('Content-Type', 'text/xml');
        request.setHeader('SOAPAction', 'update');   			 
         String b = '<?xml version="1.0" encoding="UTF-8"?>';
                b += '<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">';
                b += '<soapenv:Header>';
                b += '<ns1:SessionHeader soapenv:mustUnderstand="0" xmlns:ns1="http://soap.sforce.com/2006/04/metadata">';
                b += '<ns1:sessionId>' + UserInfo.getSessionId() + '</ns1:sessionId>';
                b += '</ns1:SessionHeader>';
                b += '</soapenv:Header>';
                b += '<soapenv:Body>';
               
                b += '<update xmlns="http://soap.sforce.com/2006/04/metadata">';
                b += '<UpdateMetadata>';
                b += '<currentName>QuoteSettings</currentName>';

                b += '<metadata xsi:type="ns2:QuoteSettings" xmlns:ns2="http://soap.sforce.com/2006/04/metadata">';
                
            	b += '<fullName>QuoteSettings</fullName>';
            	b += '<enableQuote>true</enableQuote>';
               
                b += '</metadata>';
                b += '</UpdateMetadata>';
                b += '</update>';
                b += '</soapenv:Body>';
                b += '</soapenv:Envelope>';
            request.setBody(b);
            request.setCompressed(false);
     
        //request.setHeader('Authorization', 'OAuth ' + SESSION_ID);

        String body = (new Http()).send(request).getBody();
        system.debug('Hello from body'+body);
    }

}